As a power conversion device including a step-down chopper circuit, a power conversion device described in, for example, JP 2009-189241 A is conventionally proposed.
In the power conversion device, a step-down chopper circuit is connected to an output side of a three-phase rectifier circuit, and a motor is connected to an output side of the step-down chopper circuit via an inverter. In the step-down chopper circuit, first and second capacitors are connected in series between a positive electrode-side electrode wire and a negative electrode-side electrode wire of the three-phase rectifier circuit, a first series circuit of a switching element and a diode is connected in parallel with the first capacitor, and a second series circuit of a diode and a switching element is connected in parallel with the second capacitor. One end of a reactor is connected to a connection point of the switching element and the diode of the first series circuit, and an output capacitor is connected between the other end of the reactor and a connection point of the diode and the switching element of the second series circuit.
In the step-down chopper circuit, when a short-circuit fault due to a surge voltage occurs in the first series circuit (or the second series circuit), the second capacitor (or the first capacitor) is excessively boosted, thereby possibly leading to a voltage breakdown.
In order to prevent the foregoing voltage breakdown of a capacitor of a boost chopper circuit, a DC-DC conversion device described in JP 2017-42028 A is proposed.
In the DC-DC conversion device, one ends of reactors are respectively connected to positive electrode-side and negative electrode-side of a DC power supply, and a first series circuit in which a diode and a semiconductor switching element are connected in series and a second series circuit in which a semiconductor switching element and a diode are connected in series are connected in series between a positive electrode-output electrode wire and a negative electrode-output electrode wire. The DC-DC conversion device has a configuration in which a first capacitor is connected in parallel with the first series circuit, a second capacitor is connected in parallel with the second series circuit, the other end of the positive electrode-side reactor is connected to a connection point of the semiconductor switching element and the diode of the first series circuit, and the other end of the negative electrode-side reactor is connected to a connection point of the diode and the semiconductor switching element of the second series circuit.
In the boost chopper circuit, when a short-circuit fault occurs in the first series circuit (or the second series circuit), by making the semiconductor switching element of the second series circuit (or the semiconductor switching element of the first series circuit) be in an on state, the second capacitor (or the first capacitor) is prevented from being excessively boosted and undergoing a voltage breakdown.